1. Field of the Invention
The present invention relates generally to a system for controlling damping force characteristics of respective shock absorbers of a vehicle, each shock absorber (also called a damper, but hereinafter referred to as the shock absorber) being interposed between an unsprung mass and sprung mass of the vehicle so as to provide an optimum damping force therefrom. The shock absorber is provided with changing means for changing the damping coefficient thereof at multiple stages in response to a control signal.
2. Description of the Background Art
A Japanese Patent Application First Publication No. Showa 61-163011 exemplifies a previously proposed damping characteristic controlling system for a vehicle.
In the disclosed Japanese Patent Application First Publication, a sprung mass vertical velocity and a relative velocity between sprung mass (vehicle body) and unsprung mass (tire wheel) are determined. When both velocities have mutually the same sign, the characteristics of the damping forces for any one or more shock absorbers are set to provide hard characteristics. When both velocities have the different signs (+ or -), the characteristics of the damping forces for the shock absorbers are set to provide soft characteristics. This setting operations are based on the damping force characteristic control called "Sky Hook" theory and carried out independently of four tire wheels.